1. Field of the Invention
The present invention relates to the structure of a tilt detector that is used in products having an orientation detecting function and used in various kinds of portable electronic equipment, home game machines, toys, etc.
2. Description of the Related Art
FIGS. 8-10 show the structure of a conventional tilt detector. FIG. 8 is an exploded perspective view of the tilt detector. FIG. 9 is its vertical sectional view as viewed from one side. FIG. 10 illustrates how a spherical movable contact operates.
As shown in FIGS. 8 and 9, the conventional tilt detector is composed of an insulative substrate 11 made of an insulative material, first fixed contacts 12a and 12b that are conductive metal plates and are mounted on the insulative substrate 11 so as to be parallel with each other, second fixed contacts 13a and 13b that are disposed adjacent to the first fixed contacts 12a and 12b so as to be parallel with each other, a spherical movable contact 14 that is made of a conductive metal and is to be in or out of contact with the first fixed contacts 12a and 12b and the second fixed contacts 13a and 13b, and a box-shaped case 15 that is made of an insulative material such as a synthetic resin and is attached to the insulative substrate 11 so as to cover it.
The two first fixed contacts 12a and 12b are mounted on the insulative substrate 11 so as to be opposed to each other. Similarly, the two second fixed contacts 13a and 13b are mounted on the insulative substrate 11 so as to be adjacent to the first fixed contacts 12a and 12b and opposed to each other. The interval between the first fixed contacts 12a and 12b and the interval between the second fixed contacts 13a and 13b are smaller than the diameter of the spherical movable contact 14. Therefore, the spherical movable contact 14 rests on the top surfaces of the first fixed contacts 12a and 12b or the second fixed contacts 13a and 13b so as to bridge those.
The operation of the above-configured tilt detector will be described below. As shown in FIG. 10, in a state that a device incorporating the tilt detector is inclined rightward, the spherical movable contact 14 rolls on the fixed contacts in the tilt direction (rightward direction) of the device, whereby the first fixed contacts 12a and 12b that are located on the destination side are connected to each other by the movable contact 14. The tilt direction of the device can be detected by the connection of the right-hand first fixed contacts 12a and 12b. 
Conversely, in a state that the device incorporating the tilt detector is inclined leftward (not shown), the spherical movable contact 14 rolls on the fixed contacts in the tilt direction (leftward direction) of the device, whereby the second fixed contacts 13a and 13b that are located on the destination side are connected to each other by the movable contact 14. The tilt direction of the device can be detected by the connection of the left-hand second fixed contacts 13a and 13b. 
However, the above-described conventional tilt detector is configured in such a manner that the many fixed contacts, that is, the first fixed contacts 12a and 12b and the second fixed contacts 13a and 13b, are mounted on the insulative substrate 11. Since variations are prone to occur in the intervals between the contacts, there is a problem that the contact is unstable and hence the detection accuracy is low. Further, because of its structure, the tilt detector can detect a tilt only in two directions.
An object of the present invention is therefore to solve the above problems and thereby provide a tilt detector capable of detecting a tilt in a larger number of directions and increasing the detection accuracy through stabilized contact.
To attain the above object, the invention provides a tilt detector comprising a first case that has a housing portion and in which a first fixed contact is provided on a bottom surface of the housing portion; a second case that has a housing portion and in which a second fixed contact is provided on a bottom surface of the housing portion; and a spherical movable contact that is housed in the housing portions of the first case and the second case so as to be able to roll and that is to come into or go out of contact with the first fixed contact and the second fixed contact, wherein the first case and the second case are fixed to each other so as to form an integral body in such a manner that the first fixed contact and the second fixed contact are opposed to each other; at least one of the first fixed contact and the second fixed contact is divided; the movable contact is disposed so as to roll while bridging the first fixed contact and the second fixed contact; and contact portions where the movable contact is to contact the first fixed contact and the second fixed contact assume arc shapes, respectively.
This tilt detector can detect a tilt in a larger number of (two or more) directions. When the movable contact contacts the first fixed contact and/or the second fixed contact, the contact points always vary as the movable contact rolls along the arc-shaped contact portions. As a result, a contact failure as would otherwise be caused by variations in the contact intervals, sticking of foreign matter, or the like can be prevented.
The tilt detector may be such that both of the first fixed contact and the second fixed contact are divided into at least two parts, and at least two divisional parts of the first fixed contact and at least two divisional parts of the second fixed contact are opposed to each other in such a manner as to be deviated from each other by 90xc2x0. This structure makes it possible to detect a tilt in a larger number of (four or more) directions. When the movable contact contacts the first fixed contact and/or the second fixed contact, the contact points always vary as the movable contact rolls along the arc-shaped contact portions. As a result, a contact failure as would otherwise be caused by variations in the contact intervals, sticking of foreign matter, or the like can be prevented.
The tilt detector may further comprise a first recess and a second recess that are formed at centers of the first fixed contact and the second fixed contact so as to project toward the bottom surfaces of the housing portions, respectively, and the movable contact may come into or go out of contact with the contact portions as it rolls across the first recess and the second recess that are opposed to each other. With this structure, since all the surfaces of the recesses across which the movable contact rolls are metal surfaces and do not include resin surfaces, there does not occur static electricity due to rolling friction or the like and hence sticking of foreign matter to the spherical movable contact is suppressed. Stable contact can thus be attained.
The tilt detector may further comprise arc-shaped first openings and arc-shaped second openings that are formed by punching at centers of the first fixed contact and the second fixed contact, respectively, and contact receiving members that are metal plates and are formed on the bottom surfaces of the housing portions, respectively, so as to be opposed to each other with the first openings and the second openings interposed in between, and the movable contact may come into or go out of contact with the contact portions as it rolls in the first openings and the second openings that are opposed to each other. In this structure, metal surfaces (including no resin surfaces) are formed in the openings across which the movable contact rolls. Therefore, there does not occur static electricity due to rolling friction or the like and hence sticking of foreign matter to the spherical movable contact is suppressed. Stable contact can thus be attained.